Heating of getter material with thoriated tungsten filament



Nov. 24, 1964 J. L. M INTYRE 3,153,776

HEATING OF GETTER MATERIAL WITH 7 THORIATED TUNGSTEN FILAMENT Filed Oct. 31, 1961 F lg. I. H3 I6 522 i i I 24 L a 34 3o 4o- '4 x '1 Fig. 2.

WITNESSES INVENTOR fla James L. McIntyre 6 I MKQNEY United States Patent 3,158,776 HEATING 0F GETTER MATERIAL WITH THORIATED TUNGSTEN FILAIVIENT James L. McIntyre, Big Flats, N.Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 31, 1961, Ser. No. 149,087 6 Claims. (Cl. 313-179) This invention relates to an electron discharge device and methods of processing thereof.

It is desirable during the fabrication of most electron discharge devices to remove all materials and gases from the envelope that might subsequently reduce the operational efficiency of the electron discharge device. In an image orthicon pickup tube, the failure of the gettering system and process to remove substantially all of the gas from the tube to provide a vacuum enclosure results in a defect referred to as ion spots. These ion spots cause a fuzzy defect to be generated in the central region of the target of the tube which has a tendency to mask the image.

In the image orthicon tube, the manufacturer is limited in the amount of heat that may be applied during the outgas operation due to photoemissive materials Within the envelope. In the prior art technique of processing of image orthicons, the envelope was exhausted by a conventional vacuum pump system. The envelope and its components were raised to as high a temperature as possible without adversely affecting the photoemissive materials therein. A gettering material such as barium was flashed within the device after pumping to a given vacuum. The barium material was deposited on the inner wall of the envelope of the tube. The barium material which was flashed onto the envelope of the tube combines chemically with the residual gas in the vessel to remove foreign materials and gases and further reduce the pressure. This prior art technique was only partially successful in the removal of all gases and a large percentage of processed tubes were found to contain ion spots.

It is accordingly an object of this invention to provide an improved electron discharge device.

It is another object to provide an improved method of reducing the amount of gas within the envelope of an electron discharge device after processing.

It is another object to provide an improved method and structure of processing a tube in which temperature critical tube elements restrict the amount of heat that 'may be applied to the electron device to outgas the tube.

Briefly, the present invention accomplishes the abovecited objects by providing a filament of thoriated tungsten in that region adjacent where a flash deposit of barium gettering material is provided on the envelope of the tube. In addition, the method of processing and activating this combination gettering arrangement provides means of obtaining a reduction of contamination within the envelope.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularly in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIG. 1 shows an image orthicon tube partly in section incorporating the teachings of this invention;

FIG. 2 shows an enlarged view of a portion of FIG. 1 with portions of the envelope broken away; and

FIG. 3 is a sectional view of the structure shown in FIG. 2.

Referring now to the drawing, the electron discharge 3,158,776 Fatented Nov. 24, 1964 device illustrated in FIG. 1 comprises an envelope 10 having an exhaust tubulation 12 and leads 14 provided in the base 11 thereof. A viewing window 16 is provided at the opposite end of the envelope It) with respect to the base 11. A photoemissive surface (not shown) is provided on the interior surface of the viewing window 16 and may be of a suitable material such as cesiated antimony. A description of the image orthicon structure and operation is given in the book Electronic and Radio Engineering by F. E. Terman, fourth edition.

An electron gun structure 20 is provided within the envelope 10 near the base 11 of the tube and consists of means for generating an electron beam for scanning the target member (not shown) of the tube. A plurality of secondary emissive dynode structures including elements 22 are positioned around the periphery of the electron gun 20 for collecting and amplifying the return electron beam. The output signal is derived from an anode or collector 23. A support member 24 is provided adjacent the base 11 for support of the gun 20.

The gettering system of the tube consists of a gettering ring 30 which includes a trough like portion facing the envelope wall. The trough of the ring 30 is filled with a suitable gettering material such as barium. Positioned adjacent the gettering ring 30 is a filament 34 of -a suitable material such as thoriated tungsten. In the particular embodiment shown, the filament 34 consists of about 10 turns of 11 mil diameter wire with the turns having a diameter of about 50 mils. One end of the filament 34 is connected to the support member 24 by means of lead 36 while the other end of the filament 34 is connected by means of lead 38 to an external terminal of the tube. The support member 24 is also connected to an external terminal.

After the elements have been assembled in a device the envelope 10 is exhausted and the metallic elements within it are outgassed. Generally this is accomplished by baking the entire tube at a temperature of about 375 C. and simultaneously exhausting the envelope. During this exhaust and bake cycle the filament 34 is outgassed at 5.5 amperes for five minutes. The temperature and time of this bake is limited due to heat sensitive material in the envelope and in this specific case an antimony bead used for the photosurface is the limiting material.

After this preliminary bake and exhaust cycle, the electron gun 20 is outgassed by heating the structure by inductive heating. The cathode of the electron gun 2G is activated and the photosurface is deposited on the photocathode support surface of the tube. Also during this step the getter 30 is outgassed and the filament 34 is again outgassed by heating for a period of five minutes at a current of 5.5 ampercs.

The next step in the processing of the tube is the flashing of the barium getter material in the getter member 30 and immediately thereafter the tubulation 12 is tipped ofi. The flashing of the getter material 30 deposits a coating 40 on the envelope 19 of the tube as clearly indicated in FIGS. 2 and 3. It should be noted the filament 34- is adjacent to this deposited getter coating 40. This distance is about .5 inch.

, Following the tip ofl of the envelope, the tube is ready to be aged or activated. During the aging process the cathode is reactivated and the tube is aged for about one hour with no voltages applied thereto. This process should outgas the cathode and gunto a large extent. Now with the normal aging voltages applied to the tube, the filament 34 is connected to a source of voltage so as to pass a current of about five amperes through the filament for a. period of about one hour.

After the aging process, the tube is checked and if the tube is found to have an ion spot the getter 30 is again reflashed by inductive heating and the filament 34 is operated for one or two hours with normal aging voltages on the tube. This process will normally clean up the tube but it necessarythe tungsten filament 34 may be operated for a period of four to six hours. It should be noted that the operating current passing through the filament 34 is lower in this step than during the outgas cycle so as to reduce the outgassing of the gun structure around it during its operation in the aging process.

It is believed that the thoria in the filament 34 breaks down when heat is appliedand forms tungsten oxide and thorium. The free thorium of course is an excellent getter.

It is also believedthat the tungsten'during heating breaks ,3. The method of removing gases from an envelope comprising the steps of positioning a quantity of a gettering material within said envelope, heating said gettering material by induction heating to evaporate a coating of said gettering material on the wall of said envelope, positioning a filament of thoriated tungsten adjacent said deposited coating and heating said filament to a temperature of about 2000 C. after said envelope is tipped off to break down certain gases in said envelope so that the gases may be gettered by said coating while simultaneously gettering certain other of the gases within said envelope.

4. An electron discharge device comprising an envelope and having an electron gun assembly provided at barium will getter carbonmonoxide and carbon dioxide as well as hydrogen. It is therefore seen that the compounds formed as a result of the interaction between the tungsten and the methane provides a gas which the barium material can getter. The filament 34 is heated during the aging process to probably a temperature of about 2000 C. Due to the position of the filament 34 with respect to the coating 40, the temperature of the coating 40 will be raised to about 140 C. Heating the coating 40 will cause the barium getter to pump at a much higher rate than at room temperature. This 'getten'ng process has resulted in better tubes and less shrinkage.

While there have been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangement shown and describedand it is intended tocover in the appended claims all such modifications as fall'within the true spirit and scope of the invention.

I claim as my invention:

1. The method of decontaminating an electron discharge device whioh includes an electron gun provided at one end of an envelope comprising positioning a quantity of a gettering material within the region between said electron gun and the adjacent end of said envelope, heating said gettering material so as to deposit a coating of said getten'ng material onthe wall of said envelope, positioning a filament of thoriated tungsten adjacent said deposited coating and heating said filament to a temperature of about 2000 C. after said tube is tipped off to break down certain gases in said envelope so that the gases may be 'gettered by said getter coating while simultaneously gettering certain other of the gases within the envelope.

2. 'An image orthicon pickup tube comprising an envelope and having an electron gun assembly provided at one ,end of said envelope with leads from said electron gun. assembly passing through the base end portion of said' envelope, a gettering material positioned within the region between said electron gun and said base portion capable of being flashed by RF induction heating to deposite an evaporated'coating of said gettermaterial on the wall of said image orthicon envelope'adjacent the region defined between said electron gun and said base portion, a filament of thoriated tungsten provided within the region between said electron gun structure and said base portion and positioned adjacent to said deposited getter coating and means for heating said filament by passing current therethrough to raise the tem- 6 perature of said filament to about 2000 C. and simultaneously raising the temperature of said deposited coating to a temperature higher than room temperature.

one end of said envelope with leads from said electron gun assembly passing through a base end portion of said envelope, a gettering material positioned Within the region between said electron gun and said base portion capable of being flashed by RF induct-ion heating to deposit an evaporated coating of said getter material on the wall of said envelope adjacent the region defined between said electron gun and said base portion, a

thoriated tungsten wire provided within the region between said electron gun structure and said base portion and positioned adjacent to said deposited getter coating, means for passing current through. said wire to raise the temperature of said wire to about 2000 C. and simultaneously heating said deposited coating by said wire to a temperature higher thanroom temperature.

5. The method of decontaminating an electron discharge device which includes an electron gun provided at one end of an envelope comprising positioning a quantity of barium gettering material within the region of said electron gun, heating said gettering material so as to deposit a coating of said gettering material on the wall of said envelope, positioning a filament of thoriated tungstenadjacent said deposited coating and heating said filament to a temperature of about 2000 C. after said tube is tipped off to break down certain gases in said envelope so that the gases may be gettered by said getter coating while simultaneously gettering certain other of the gases within the envelope.

' 6. An image orthicon pickup tube comprising an envelope and having an electron gun assembly provided at one end of said envelope with leads from smd electron gun assembly passing through the base end portion of said envelope, a barium gettering material positioned tion and positioned adjacent to said deposited getter coating, means for heating said filament by passing current therethrough to raise the temperature of said mament to' about 2000 C. and simultaneously raising the temperature of said deposited coating to a temperature higher than room temperature by radiated heat from said filament.

References Cited in the file of this patent UNITED STATES PATENTS 1,244,217 Langmuir on. 23, 1917 1,993,767 Allen Mar. 12, 1935 2,804,564

Couch Aug. 27, 1957 

3. THE METHOD OF REMOVING GASES FROM AN ENVELOPE COMPRISING THE STEPS OF POSITIONING A QUANTITY OF A GETTERING MATERIAL WITHIN SAID ENVELOPE, HEATING SAID GETTERING MATERIAL BY INDUCTION HEATING TO EVAPORATE A COATING OF SAID GETTERING MATERIAL ON THE WALL OF SAID ENVELOPE, POSITIONING A FILAMENT OF THORIATED TUNGSTEN ADJACENT SAID DEPOSITED COATING AND HEATING SAID FILAMENT TO A TEMPERATURE OF ABOUT 2000*C. AFTER SAID ENVELOPE IS TIPPED OFF TO BREAK DOWN CERTAIN GASES IN SAID ENVELOPE SO THAT THE GASES MAY BE GETTERED BY SAID COATING WHILE SIMULTANEOUSLY GETTERING CERTAIN OTHER OF THE GASES WITHIN SAID ENVELOPE. 